#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>

int main()
{
    int score = 0;
    scanf("%d", &score);
    if (score >= 90 && score <= 100)
        printf("A\n");
    else if (score >= 80 && score <= 89)
        printf("B\n");
    else if (score >= 70 && score <= 79)
        printf("C\n");
    else if (score >= 60 && score <= 69)
        printf("D\n");
    else if (score >= 0 && score <= 59)
        printf("E\n");
    else
        printf("F\n");
    return 0;
}